The present invention relates to a signal processing device, a signal processing method and a sound emitting system for utilizing a subwoofer for emitting a sound on a low-pitched sound side and a speaker for emitting a sound on a high-pitched sound side higher than the subwoofer in combination to emit a sound.
Recently, it is done in the home theater, or the like that the frequency characteristics of the sound signals fed to respective speakers should be adjusted to reproduce a better sound. For example, in Patent Literature 1, such an approach is set forth that a balance between a mid-pitched sound and a low-pitched sound is adjusted by lowering a sound volume in the mid-pitched sound and shifting a cut-off frequency to the high-pitched sound side. However, such a problem arises that, when the sound volume in the mid-pitched sound is lowered, the low-pitched sound is emphasized and thus localization of sounds is changed or a feeling of localization is lacking. Therefore, in Patent Literature 1, the approach of restoring a feeling of localization of sounds to its original state by increasing a sound volume in a predetermined band (1 to 8 kHz) on the mid-pitched sound side is also set forth.    [Patent Literature 1] JP-A-2000-197182
Meanwhile, in order to compensate the low-pitched sound side that cannot be sufficiently reproduced by the ordinary speaker, in many cases the subwoofer for emitting exclusively the sound in the low-pitched sound side is added to the sound emitting system in the home theater, or the like. In many cases, the subwoofer is placed in the direction except the forward front direction when viewed from the listening position. A boundary (crossover frequency) of the frequency bands that are assigned to both speakers respectively is set between the subwoofer that emits the sound in the low-pitched sound side and the speaker that emits the sound the mid-pitched sound side. Normally, a crossover frequency is set depending on a low-pitched sound reproducing ability of the speaker that emits the sound in the mid-pitched sound side.
In the home theater, or the like, many users desire to emphasize the low-pitched sound much more, and thus a sound volume of the subwoofer is often increased relatively. When a sound volume of the subwoofer is increased, the subwoofer has charge of the sound emission up to the band in excess of a crossover frequency (mid-pitched sound side)(see a solid fine line in FIG. 2). Therefore, such a problem is caused that the localization of sounds is moved to the subwoofer side (the direction other than the forward front direction) or a feeling of localization is lacking.
Also, there exists such a problem that, when a sound volume of the subwoofer is increased, a sound quality is degraded (a strange feeling is produced in an auditory sense). That is, such a problem arises that, when only a sound volume of the subwoofer is increased, a balance of sound volume between the subwoofer and the speaker is lost in the band in excess of the crossover frequency.
In Patent Literature 1, merely the control of the cut-off frequency and the sound volume is applied to the mid-pitched sound side. Therefore, a balance of sound volume is still lost in the band that exceeds the crossover frequency or more. Namely, the problem caused due to a difference in a reproducing ability between the subwoofer and the speaker is not considered. It is still impossible to say that the problems of localization of sounds and degradation of sound quality are solved. Also, such a problem arises that, when only a certain band is emphasized as in Patent Literature 1, a balance of sound volume in the band in excess of the crossover frequency becomes worse furthermore.